On Ionization Effects and Abundance Ratios in Damped Lyα Systems
On Ionization Effects and Abundance Ratios in Damped Lyα Systems
复制标题
阻尼 Lyα 系统中的电离效应和丰度比
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
C. Charbonnel
中科院分区：
文献类型：
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作者：
Y. Izotov;D. Schaerer;C. Charbonnel
在阻尼Lyα系统（DLAs）中观察到的Al III和单电离物种的速度结构之间的相似性表明在大多数金属吸收线形成的区域中存在电离气体。一个简化的模型，包括（区域1）的平面平行电离有界的内部辐射场照射的区域和（区域2）的中性区域与金属含量可以忽略不计被认为是。我们计算光电离平衡模型区域1和约束的电离参数所观察到的N（Al III）/N（Si II）柱密度比。在这些条件下，我们发现电离效应是重要的。如果考虑到这些影响，DLAs中的元素丰度比与银河系恒星和本地低金属丰度蓝矮星系的H II区的观测结果相当一致。特别是，我们不能排除在DLAs和贫金属星系相同的主要N起源。虽然我们的模型并不排除尘埃颗粒上的重元素存在少量的损耗，但我们并不需要援引这些损耗。虽然高度简化，并依赖于一个显着较低的金属含量在区域2的强有力的假设，我们的模型似乎是支持最近的数据上的本地DLA，它是不矛盾的高红移DLAs与目前的知识。如果是正确的，它提供了一个清晰的简化理解重元素丰度比在DLAs和他们的比较与当地的宇宙。
The similarity between observed velocity structures of Al III and singly ionized species in damped Lyα systems (DLAs) suggests the presence of ionized gas in the regions where most metal absorption lines are formed. A simplified model consisting of (region 1) a plane-parallel ionization bounded region illuminated by an internal radiation field and (region 2) a neutral region with a negligible metal content is considered. We calculate photoionization equilibrium models for region 1 and constrain the ionization parameter by the observed N(Al III)/N(Si II) column density ratio. Under these conditions we find that ionization effects are important. If these effects are taken into account, the element abundance ratios in DLAs are quite consistent with those observed in Milky Way stars and in H II regions of local low-metallicity blue compact dwarf galaxies. In particular, we cannot exclude the same primary N origin in both DLAs and metal-poor galaxies. No depletion of heavy elements on dust grains needs to be invoked, although our models do not exclude the presence of little depletion. Although highly simplified and relying on the strong assumption of a significantly lower metal content in region 2, our model appears to be supported by recent data on a local DLA, and it is not in contradiction with the current knowledge on high-redshift DLAs. If correct, it offers a clear simplification in the understanding of heavy element abundance ratios in DLAs and their comparison with the local universe.